(d) Fluoroscopy

Attempts were made to visualize movement of the gastric mill during aggressive behaviour using fluoroscopy. Five live crabs were imaged (Hologic 9900 OEC c-arm) in the Radiology unit at Hillcrest Medical Center, UCSD. Oral contrast (dilute barium) was administered to crabs through the buccal region using a syringe. To permit transmission of X-rays, crabs were recorded in a clear acrylic box (39 × 23 × 23 cm) placed on a table directly under the X-ray c-arm. X-ray imaging was processed at a rate of 15 frames s⁻¹. Aggressive behaviour of crabs was induced by either approaching the crab with a net handle or adding a second live crab to the box. Video frames were examined for gastric mill activity using MicroDicom viewer (v. 2.8.3, Sofia, Bulgaria).